The moisture-proof cabinet of Shanghai Huanzheng Test Equipment Factory adopts the method of adsorption intermittent continuous dehumidification. It is a method of removing moisture from the air using a solid desiccant. The characteristic of this method is: neither cooling air nor compressing air, no noise, environmental protection and energy saving. The movement and the control display circuit are integrated with the sealed container, and the wet substance and the hygroscopic adsorbent are placed to adsorb the moisture inside the wet substance. Since the water is regarded as a molecular state, the water molecules are very Actively and continuously, it evaporates and spreads on the surface of the material. Due to the action of the adsorbent, these water molecules are slowly accumulated in the adsorbent. The humidity inside the closed container during the transfer process is almost constant. When the dehumidification capacity of the adsorbent approaches an equilibrium state, the concentration of water in the air and the amount of water in the substance are close to equilibrium, and the amount of water in the substance does not change to reach equilibrium. The movement of moisture does not occur between the two. Shanghai Huanjing adopts the control method, closes the desiccant suction door to open the water vapor diffusion door, heats the adsorbent saturated with moisture, removes the moisture in the air, and naturally evaporates into the air outside the box for regeneration and desorption. Fully desorbing allows the adsorbent that has reached saturation to be regenerated, through moisture absorption and dehumidification, control door switching, continuous dehumidification of humid air in the closed box to achieve a new balance, repeated intermittent continuous circulation to achieve the purpose of drying. Due to its small volume, low adsorption dose, repeated regeneration, and almost automatic operation, once it is energized, no special operation is required.
HUMGINE moisture-proof cabinet system takes the single-chip microcomputer as the core, converts the humidity in the humidifier into capacitance through the capacitive polymer humidity sensor, and then converts it into voltage signal through the humidity-voltage converter, and processes it through A/D conversion and single-chip processing. The latter signal is used for humidity display. The suction door is normally open, and the wet door is normally closed. When the moisture absorption of the molecular sieve in the container reaches saturation, the humidity in the container does not change at this time. If the humidity value is not the same as the set humidity value, the difference between the two humidity values ​​is processed by the single chip microcomputer to generate a trigger signal. Under the trigger of the signal, the pulse current circuit of the control memory alloy spring is turned on to heat the electric heating plate outside the memory alloy, and also to heat the electric heating plate under the molecular sieve. In the CD4541 chip that controls the pulse current, we set a threshold value for the energization heating time of the electric heating plate. The heating time is determined by the performance index of the memory alloy spring. After the heating time is reached, the alloy spring is heated to a set length. At this time, the phase change caused by the heat of the spring can accurately control the opening and closing of the wet door and the moisture absorption door to alternately change. The memory alloy spring is deformed by heat to control the opening and closing of the suction door and the wet door. The alloy spring is heated first to close the suction door, and the wetted hole is also closed to prevent external humid air from entering the inside of the instrument. After the moisture absorption door is completely closed, the alloy spring continues to be thermally deformed, and the control wet door is opened, and the moisture absorption door is completely closed. The molecular sieve is heated, and the absorbed water is evaporated by heat, and the water vapor is discharged through the wet door. When the heating time is reached, the energization is stopped, the memory alloy spring is cooled, and the state is restored to the state before the heating, so that under the action of the spring force, the wet door is first closed, and the moisture absorption door is opened after the wet door is completely closed, so that the molecular sieve is again Place in the air inside the instrument and continue to absorb moisture. The moisture absorption and dehumidification are repeated so that the humidity in the humidity control device reaches the set standard.
The main polymer humidity sensor of the humidity control movement, the automatic temperature control memory alloy spring and the hardware realization circuit are composed of three parts.
(1) Automatic temperature controlled memory alloy spring
Shape memory alloy is a new functional material integrating sensing, driving and material/structure. Its main feature is shape memory effect, which can sense the change of temperature and displacement, and convert thermal energy into mechanical energy. The ability to sense, perform, judge, and adapt the alloy material/structure can be achieved by controlling heating or cooling. Generally, the memory alloy is plastically deformed at a low temperature, and after the temperature rises, it overcomes the plastic deformation and returns to the shape of the memory. The material of the spring designed and controlled by Shanghai Huanjing to open and close the wet door and the suction door is a NiTi shape memory alloy. The spring has the following six states during operation: 1 control the suction door to open, the wet door is completely closed; 2 control the suction door from open to closed state, the process wet door is still closed; 3 when the suction door is completely closed , the control of the wet door transition from closed to open state; 4 control the wet door is completely closed, the wet door is open. 5 In the state that the suction door is completely closed, the control of the moisture discharge door is transitioned from the open state to the closed state; 6 when the moisture release door is completely closed, the control moisture absorption door is closed to the open state. Shanghai Huanjing uses the principle of automatic temperature-controlled memory alloy spring electric heating to control the opening and closing of the wet door and the suction door. When the pulse current supply circuit starts to work, the discharge current is controlled to discharge the discharge. The current passes through the electric heating plate outside the NiTi alloy memory spring, and the electric energy is converted into heat energy. When the temperature of the spring rises above the phase transition point, the spring begins to change phase and returns to the shape it remembers. L + shrinks to the memory length L. Under the action of the phase change force of the alloy memory spring, the suction door is closed, but the force generated by the phase change of the tension spring is not enough to open the wet door. The electric heating plate continues to be energized and heated, and after the suction door is completely closed, the force generated by the phase change of the tension spring begins to open the wet door. When the predetermined pulse current supply time is reached (the setting of the power supply time is controlled by the chip CD4541B), the current on the hot plate is canceled, and the temperature of the NiTi alloy memory spring is lowered by the cooling effect of the working environment medium to below the phase transition point. For a spring with a two-way memory effect, the spring will automatically extend to the position of L + , and the wet door will be closed under the action of the tension spring restoring force and the memory alloy spring force. After the wet door is completely closed, the moisture absorption door is alloyed. Open under the action of the memory spring. The reciprocating of the current through the pulse current supply circuit, because the phase change of the shape memory alloy occurs in a certain temperature range instead of a fixed temperature point, in this system we use a part of the shape recovery, so that the spring stretches When positioned in a fixed position, the shape of the alloy memory spring heated can accurately control the closed and open state of the wet door and the suction door.
(2) Hardware implementation circuit
The hardware implementation circuit of the whole system is composed of humidity sensor, humidity-voltage converter, A/D conversion, humidity setting circuit, single-chip microcomputer and display and memory alloy spring drive control part. Can be divided into two parts: pre-circuit, signal conditioning, data acquisition, signal processing and pulse charging current supply circuit. The basic design idea is to realize the humidity test by the principle that the dielectric constant of the polymer film humidity sensitive capacitor changes with the relative humidity of the ambient gas to change the capacitance. This part of the circuit uses high stability DC voltage excitation by the CMOS gate. The circuit constitutes a pulse width difference measuring circuit of the synchronous resonant oscillator, and the capacitor/voltage conversion is obtained by rectifying and filtering, and the voltage proportional to the humidity change is converted into a current signal of 4-20 mA, and finally the current signal is passed through the data collecting end. Converted to DC voltage signal, sent to A/D converter for data acquisition and display. The drive control circuit for the memory alloy spring is mainly composed of CD4017BE, CD4541BE, vacuum diode circuit and signals from the humidity sensor.
(3) Polymer humidity sensor
The polymer material humidity sensor is the most widely used sensor in the humidity sensor. It has abundant material sources, simple manufacturing process, no need for heating and cleaning, wide application range, strong practicability, superior performance in other sensors, and wide humidity range. Short response time, small hysteresis hysteresis, small temperature coefficient and long service life. In the system design, Shanghai Huanjing uses a capacitive polymer humidity sensor. The moisture sensitive membrane used by Shanghai Huanjing is cellulose acetate butyrate. The moisture sensitive material has the following characteristics: 1 a practical sensitivity output, from low humidity to high humidity corresponding to the change of relative humidity, the sensitivity changes linearly; 2 in the process of moisture absorption and desorption, the sensor output hysteresis is small; 3 temperature The coefficient is small; 4 is long-term stable; 5 sensor output is not affected by other gases; 6 such moisture-sensitive material is simple to make.
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